Manufacture of aluminum articles with anodized surfaces presenting multicolor effects



Nov. 8. 1966 H FROMSON 3,284,321

MANUFACTURE OF ALUMIMUM ARTICLES WITH ANODIZED SURFACES PRESENTING MULTI-COLOR EFFECTS Filed July 1-9 1962 maid- I l.. 7 INVENTOR HOA R0 A. FRO/750M United States Patent Office 3,284,321 Patented Nov. 8, 1966 3,284,321 MANUFACTURE OF ALUMINUM ARTICLES WITH ANODIZED SURFACES PRESENTING MULTI- COLOR EFFECTS Howard A. Fromson, Rogues Ridge Road, Weston, Conn. Filed July 19, 1962, Ser. No. 210,908 18 Claims. (Cl. 204-45) The present invention relates to the manufacture of aluminum articles with anodized surfaces present-ing multi-color effects. In the specification and claims herein, when reference is made to a materialas being of aluminum, it is intended, unless otherwise specified, that the material be either of substantially pure aluminum or of an aluminum alloy containing a predominant proportion of aluminum.

One way to color the surface of an aluminum article is to anodize the surface to form a porous anodic coating thereon comprising aluminum oxide, dyeing the coating with a dye and then sealing the dyed coating to render it non-absorptive by immersing the article in hot water or subjecting it to steam, a step which converts the aluminum oxide to impermeable aluminum oxide monohydrate. In the specification and claims, any unqualified reference to sealing is intended to designate the operation of sealing by hydration at elevated temperatures, as for example, by the use of hot water or steam.

Another way to color an aluminum article is to depend on the color imparted by the anodizing step without the use of a dye. An aluminum article, for example, when subjected to certain anodizing electrolytes, may be colored merely by the anodizing process alone, depending on the character of the electrolyte and/ or the composition of the article.

In anodizing an aluminum article, the article is placed on a rack for immersion in the anodizing bath. Where it has been desired to create a multi-color effect on the surface of the aluminum article, it has been necessary to subject the article to excessive handling, including the removal of the article from the rack and its return to the rack, where a number of immersion steps have been involved. This handling is time consuming and may mar the article in the process of handling.

One object of the present invention is to provide a new and improved process of decorating the surface of an aluminum article with multi-color patterns and effects with minimum of direct handling of the article.

Another object of the present invention is to provide an aluminum article having a surface with new and improved multi-color effects produced by the process of the present invention.

In the specification and claims, a surface is considered to be multi-colored when two or more areas thereof differ in any one of the three dimensions of color, namely hue, value and/or intensity or purity, sometimes referred to as chroma.

In accordance with certain features of the present invention, the surface of the aluminum article to be decorated has a certain area intended to form a pattern of one color. This area is masked off with an acid resistant material. After the resistant mask is applied, the adjoining exposed area of the surface of the aluminum article, intended to form a pattern of a color different from that intended for the masked area is anodized by immersion in an oxidizing electrolytic bath. The resistant mask is then removed preferably by means of a solvent, and the article is again anodized in an oxidizing electrolytic bath. The three steps of first anodizing, removing the resistant mask and then anodizing again, is desirably carried out without removing the article from the portable supporting rack, the steps merely requiring the article while on the rack to be transferred from one bath to another, whether the bath is an anodizing electrolyte, a rinsing bath, a mask removing solvent, or a dyeing bath.

One way in which multi-color effects can be produced by the process described in accordance with the present invention is to mask the area intended to form a pattern of one color with an acid resistant material. This acid resistant material may, for example, be asphaltum or an epoxy resin applied directly to the area intended to form a pattern of one color or may be masking tape impregnated or coated with an acid resistant material, such as asphaltum or an epoxy resin. While this masking material is on the surface of the article, and while the article is on the rack, the article is immersed in a first bath of anodizing electrolyte. This operation anodizes the exposed area of the article while the masked area remains unafiected. The anodizing electrolyte will cause the exposed area to assume a color whose characteristics will vary according to the nature of the electrolyte or to the composition of the aluminum article. In order to fix this color, and to prevent the latter anodizing step from affecting it, the anodized surface may be sealed. The anodized surface when sealed is nonporous, so that when the article is subjected to the second anodizing step, the anodized and sealed surface will not be affected by the electrolyte employed in this second anodizing step.

With the aluminum article anodized and sealed in the exposed area, the resistant mask is removed by stripping, if it is a tape or by a solvent where the mask is a liquid, such as asphaltum or an epoxy resin, applied directly to the article. This removal is desirably effected while the article is still on the rack in which it was supported while being anodized. Where the removal of the mask requires a solvent, this mask is removed preferably by immersing the article in a solvent bath. Where the mask is asphaltum applied directly to the surface of the aluminum article, the solvent may be kerosene or conventional mineral spirits.

With the anodized article stripped of the masking and while the aluminum article is still retained on the rack, the article is subjected to the action of a different anodizing electrolyte, which applies to the previously masked area a color different from that applied to the previously anodized area, without colorably affecting this previously anodized area. This latter anodized area is desirably sealed.

Each of the anodizing steps may be carried out for periods ranging between 1 to 150 minutes depending on the character of the electrolyte.

As a result of the process of the present invention described, there is produced a decorative surface having two precise patterned areas of different colors attained primarily by anodizing action, without the use of dyes, and with minimum of handling of the article and with minimum of time consumption.

One of the anodizing steps may be carried out by oxidizing electrolyte of the conventional type, such as one consisting essentially of the usual aqueous solution of sulfuric acid. This anodizing electrolyte will produce a clear silver color on the aluminum article. This electrolyte may comprise 12 to 18% by weight of sulfuric acid, and may be employed at a temperature of 68 to F. at a current density of 12 to 18 amperes per square foot, for as short a period as five minutes, and for as long a period as one hour, where heavier oxide films are desired.

The other anodizing step may be carried out by an electrolyte solution of the type described in United States Patent 3,031,387, in conjuction with one of the aluminum alloys described in said patent. The patent indicates that if one of the aluminum alloys specified therein is subjected to an anodizing step with an aqueous solution consisting essentially of from to 50% by weight of sulfosalicyclic acid, at least one substance selected from the group consisting of metal sulfates and sulfuric acid in an amount equivalent to from about 0.1 to 4% sulfuric acid and the balance water, that the color produced will be silvery gray, tan, light blue gray, dark gray black, brown gray, golden brown, jet black and dark blue black, depending on the composition of the aluminum alloy. This electrolyte is desirably maintained at a temperature ranging from 55 to 85 F. for a period ranging from 1 to 150 minutes at an initial current density of from about to 100 amperes per square foot and a voltage of from about 20 to 120 volts.

A particularly decorative and attractive multi-color effect is silver and black, which can be obtained with an aluminum article of an alloy designated in the aforesaid patient as alloy 5086 and alloy 606 l-T6; alloy 5086 as indicated in said patent and as fixed by the Aluminum Association contains copper 0.1%, iron 0.5%, silicon 0.4%, manganese 0.20.7%, magnesium 3.5-4.5%, zinc 0.25%, chromium .()i50.25% and titanium 0.15%; alloy 6061-T6 as indicated in said patent and as fixed by the Aluminum Association contains copper 0.15-0.40%, iron 0.7%, silicon 0.40.8%, manganese 0.15%, magnesium 0.81.2%, zinc 0.25%, chromium 0.15-0.35% and titanium 0.15%. For use with these alloys 5086 and alloy 6061T6, in order to produce a black color, the anodizing electrolyte may consist essentially of an aqueous solution of from 7 to by weight of sulfosalicyclic acid, and at least one substance selected from the group consisting of metal sulphates and sulfuric acid in an amount equivalent to from about 0.3 to 4% by weight of sulphuric acid, and the anodizing operation may be carried out at a temperature ranging from about 55 to 85 F. and at a current density of from about 10 to 100 amperes per square foot and voltages from about to 120 volts for a period of from 20 to 60 minutes.

If any color other than black is desired for one of the patterned areas of the aluminum article, any other of the alloys described in the aforesaid patent may be employed for said article, and the conditions for anodizing said area may be that indicated in said patent to obtain any of the colors referred to in said patent as being obtained with these other alloys.

The basic process of the present invention, namely, the masking of a predetermined area of the surface'of an aluminum article, the anodizing of the exposed area of the surface, the stripping of the mask and the anodizing of the previously masked area of the surface is desirably carried out in the manner described without dyeing to produce a multi-color effect and the second anodizing step is desirably carried out after the exposed area anodized by the first anodizing step has been scaled, to fix the color produced by this first anodizing step. However, as far as certain aspects of the invention are concerned, after an exposed area is anodized by the first anodizing step and after the mask is stripped from the other area, but while the anodized area is still unsealed and, therefore, still porous, the surface of the stripped article may be subjected to the second anodizing step. This second anodizing step not only colors the previously stripped area of the aluminum article, but changes the color of the area previously anodized by the first anodizing step, as the result of the composite coloring effect of the two superimposed anodizing steps on the latter area. For that purpose, the two anodizing electrolytes may be basically different as described above, or may be basically the same, so that the difference in coloring obtained between the two areas may be the result of differences in anodizing time. For example, an electrolyte of the type referred to in the aforesaid patent, when applied to one of the aluminum alloys indicated in said patent as alloy 5357, produces a light brown color when the anodizing is for a certain period and a dark brown color when the anodizing time is increased. A design having two values or shades of brown can be applied to the surface of an aluminum article by the same or similar electrolytes, either by sealing the first anodized area before the second anodizing step, and operating the two steps for different periods, or by leaving the first anodized area unsealed while the second anodizing step is carried out, so that the final color effect on the first anodized area is the result of the two anodizing periods. The latter process is more desirable, since only one sealing step is required for both anodized areas, and since the total time consumed for effecting the two anodizing steps is shorter.

As far as certain aspects of the invention are concerned, the basic process of the invention may be employed in connection with a dyeing step. For example, after the first anodizing step with a solution of sulphuric acid has been effected on the exposed area of the masked aluminum article producing a clear or silver color, and before sealing said area, the area is dyed with any of the lightfast dyes conventionally employed in coloring aluminum oxide or anodized surfaces, such as for example, as phthalocyanine dyes, azo dyes, and ferric ammonium oxalate. The dyeing is effected by dipping the aluminum article into the bath of dye solution after the exposed area of the surface of the article has been anodized and before the area has been sealed or the article stripped of its mask. After rinsing to remove the excess dye solution, the dyed area of the aluminum article is sealed by hydration at elevated temperatures to fix the dyed color. The mask is then stripped from the aluminum article in the manner described through the use of a solvent, and the area previously masked is subjected to an anodizing step with or without dyeing to color said area differently from the first anodized area.

The sealing referred to in all of the possible embodiments described may be carried out at elevated temperatures, for example, in water, at to 212 F. at a pH of 5 to 6, and the time of immersion may be 5 to 40 minutes. If desired, nickel acetate, cobalt acetate, or any other suitable agent may be added to the sealing water in small concentrations, for example, in the order of .1 to .5 of the sealing agent, especially in cases where one of the areas has been dyed and it is desired to prevent the dye from bleeding or leaching during the sealing operation.

In some operations under the present invention, the first area anodized need not be sealed before the previously stripped area is anodized, especially where no dyeing of either areas is involved, and where it is desired to superimpose the second anodization upon the first anodization for the purpose described, or where the second anodization is such that it cannot change the color of the first anodized area. In the latter case, for example, the first anodizing step may color the exposed area black, in which case any anodization superimposed upon the first anodization will not change the black color. Even where the previously masked area is to be dyed after being anodized, the oxide formed on the first exposed area by the electrolyte, especially of the type employed in the aforesaid patent, and particularly when the electrolyte is such as to color the area black, is so dense, that it cannot dye, even if unsealed, so that sealing is not necessary before subjecting the masked and anodized area to dyeing.

In the accompanying drawings, there is shown for the purpose of illustration, a conventional rack on which the aluminum article may be supported while being subjected to the step of the process. In these drawings,

FIG. 1 is a perspective of the rack showing the aluminum article supported thereon, and

FIG. 2 is a section of the rack taken on lines 2-2 of FIG. 1, but on a larger scale.

Referring to the drawings, the rack comprises an I- beam 10 having high electrical conductivity, such as aluminum, secured to a suitable source of anodizing current through a connector 11 and having a series of contact rods 12 secured to and depending from the lower flange of the beam. An aluminum article 13 to be treated by the method of the present invention, shown in the form of a sheet covered in certain areas with an acidresistant mask 14, is supported on and secured to the rods 12 by means of clamps 15. The beam has eye bolts 16 by which the rack can be lowered into an anodizing bath, rinsing bath, dyeing bath, sealing bath or mask removing solvent bath, through lowering and lifting chains 17.

The invention may be illustrated by the following examples.

Example 1 A sheet of aluminum alloy 5086 is immersed in an alkaline cleaning bath of a conventional type as, for example, a solution of trisodium phosphate, to free the patterned surface of grease and other extraneous materials without substantially etching the surface thereof. The cleaning solution may consist, for example, of 4-0- grams per liter of sodium carbonate, 20 grams per liter of trisod-ium phosphate, 5 grams per liter of sodium metasilicate, the balance water. The solution is maintained at a temperature of about 160 F. for cleaning. The cleaned sheet is then rinsed in cold water.

On the cleaned aluminum sheet is silk screened or printed a pattern of the desired configuration with an acid resistant material, such as asphaltum to form a mask on the area of the sheet to be coated of one color. Epoxy resin may also be used instead of asphaltum as a masking material. The masked sheet while on a conventional portable rack, such as that illustrated in the drawings, is then anodized from 20 to 60 minutes by immersion in an electrolyte bath containing an aqueous solution of from 7 to by weight of sulfosalicylic acid, and at least one substance selected from the group consisting of metal sulphates and sulfuric acid in an amount equivalent to from about .3 to 4% by weight of sulfuric acid at temperatures from about 55 to 85 F. and at a current density of from about 10 to 100 amperes per square, and voltages from about to 120 volts. More specifically, the sheet is anodized in an electrolyte bath consisting of 10% by weight of sulfosalicylic acid, 0.5% by Weight of sulfuric acid and the balance water. The anodizing bath is maintained at a tempearture of 77 F. Anodizing begins with a current density of 24 amperes (D.C.) per square foot of work surface and the anodizing is continued at this current density until the cell voltage reaches a maximum of 65 volts in 25 minutes. The voltage is maintained at this maximum value for an additional 15 minutes, so that the total anodizing time is 40 minutes.

The areas of the aluminum sheet which have been exposed to the electrolyte in the manner described are converted to a deep black color which is light-fast. After anodizing as described, the aluminum sheet while still in the rack is sealed in hot water at a temperature of 200 F. with a pH of 5.5 for a period of 20 minutes.

The aluminum sheet while still on the rack is immersed in a stripping bath to strip the surface of the asphaltum mask. This bath may consist of a solvent type stripper such as kerosene or conventional mineral spirits.

After the stripped sheet is rinsed, it is immersed in an anodizing solution consisting essentially of 15% by weight of sulfuric acid at a temperature of 74 F. at a current density of 15 amperes per square foot and a voltage of about 60 volts. The sheet is anodized for a period of minutes, and the areas outside of the black areas will be colored silver.

The sheet is then sealed while still on the rack in hot water at a temperature of 200 F. with a pH of 5.5 for a period of 20 minutes.

The results of the treatment of Example 1 described is an anodized pattern of silver and black, the areas anodized with sulfosalicylic acid solution being black and the areas anodized with sulfuric acid solution being silver. The results are extremely pleasing and comparatively inexpen sive to achieve.

Example 2 Example 1 is followed up to the point where the sheet has been anodized black with sulfosalicylic acid solution, sealed, stripped of its masking, anodized in silver color with sulfuric acid solution but short of the last sealing step. After the last anodizing step with sulfuric acid solution, the aluminum sheet while still on the rack is rinsed and then immersed in a dyeing bath consisting essentially of 0.2% aqueous solution of Vitrolan Red Gre (C.I. Acid Red 183; CI. 18800), a monoazo metallized dye comprising a chromium complex, at a temperature of F. for about 4 minutes. By this dyeing operation, the silver colored areas will be dyed red, while the previously black anodized and sealed areas will not be colorably affected. The aluminum sheet colored black and red is then sealed in hot water at F. containing 5 grams per liter of nickel acetate and 1 gram per liter of cobalt acetate.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto but is to be construed broadly and restricted solely by the scope of the appended claims.

What is claimed is:

1. In a process of producing a multi-color effect on the surface of an aluminum article, the combination of steps comprising applying a resistant mask to a predetermined undyed area of said surface while leaving another undyed area exposed, anodizing the exposed area by treatment in an anodizing electrolytic bath, stripping the mask from the article, and anodizing the stripped area of the surface by treatment in an anodizing electrolytic bath, while the previously anodized undyed area is also exposed to the latter bath, the two anodizing steps being carried out under conditions to produce different colorations in the two anodized areas resulting solely from anodization of both of said areas by the end of the second anodization period.

2. In a process as described in claim 1, at least one of said areas being left undyed and with a color corresponding to the color imparted to said one area by the anodizing step applied thereto.

3. In a process as described in claim 1, both of said areas being left undyed and with respective colors corresponding to the colors imparted to said areas by the anodizing steps, the conditions for the two anodizing steps being such as to produce contrasting colors in said areas.

4. In a process as described in claim 3, said electrolytic baths being of different compositions to produce contrasting colors in said areas resulting from difierences in said composition.

5. In a process as described in claim 10, the second area anodized being dyed and sealed after being anodized a color other than the color of the area first anodized.

6. In a process as described in claim 1, the first of said anodizing steps being carried out With an electrolyte containing sulfosalicylic acid and a substance selected from the class consisting of metal sulphates and sulfuric acid to produce on the area anodized thereby in conjunction with the added action of the electrolytic bath employed for the second anodizing step on the latter area a color darker than silver, the second of said anodizing steps being carried out under conditions to color the area previously masked a lighter color.

7. In a process as described in claim 1, said aluminum article being made of an alloy of the class consisting of alloy 50186 and 6061T6, and the first of said anodizing steps being carried out with an electrolyte containing sulfosalicylic acid and a substance selected from the class consisting of metal sulphates and sulfuric acid to produce on the area anodized thereby in conjunction with the added action of the electrolytic bath employed for the second anodizing step on the latter area a color darker than silver, the second of said anodizing steps being carried out under conditions to color the area previously masked a lighter color.

8. In a process as described in claim 1, said aluminum article being made of an alloy of the class consisting of alloy 5086 and 6061-T6, and the first of said anodizing steps being carried out with an electrolyte containing an aqueous solution of from 7 to 15% by weight of sulfosalicylic acid, and at least one substance selected from the group consisting of metal sulphates and sulfuric acid in an amount equivalent to from about 0.3 to 4% by Weight of sulfuric acid to produce on the area anodized thereby in conjunction with the added action of the electrolytic bath employed for the second anodizing step on the latter area a color darker than silver, the second of said anodizing steps being carried out under conditions to color the area previously masked a lighter color.

9. In a process as described in claim 1, said aluminum article being made of an alloy of the class consisting of alloy 5086 and 6061-T6, the first of the anodizing steps being carried out with an electrolyte containing sulfosalicylic acid and a substance selected from the class consisting of metal sulphates and sulfuric acid to produce on the area anodized thereby a color darker than silver, the other anodizing step being carried out with an electrolyte of the type to color the area anodized by the latter electrolyte silver.

10. In a process as described in claim 9, said other anodizing step being carried out with an electrolyte consisting essentially of a solution of sulfuric acid.

11. In a process as described in claim 1, said aluminum article being made of an alloy of the class consisting of alloy 5086 and 6061-T6, and the first of said anodizing steps being carried out with an electrolyte containing an aqueous solution of from 7 to 15 by weight of sulfosalicylic acid, and at least one substance selected from the group consisting of metal sulphates and sulfuric acid in an amount equivalent to from about 0.3 to 4% by weight 8 of sulfuric acid, to produce on the area anodized thereby a color darker than silver, the other anodizing step being carried out with an electrolyte solution comprised of 12 to 18% by Weight of sulfuric acid to produce on the area anodized by the latter electrolyte solution a silver color.

12. In a process as described in claim 1, said aluminum article being supported on a rack before being subjected to the first anodizing step and being maintained on said rack until after the second anodizing step has been completed.

13. In a process as described in claim 10, said article being supported on a rack before being subjected to the first anodizing step and being maintained on said rack until after the second anodizing step has been completed.

14. An aluminum article having a multi-color pattern thereon produced by the process of claim 1.

15. An aluminum article having a multi-color pattern thereon produced by the process of claim 4.

16. An aluminum article having a multi-color pattern thereon produced by the process of claim 6.

17. An aluminum article having a multi-color pattern thereon produced by the process of claim 10.

18. An aluminum article having a unulti-color pattern thereon produced by the process of claim 11.

References Cited by the Examiner UNITED STATES PATENTS 2,085,988 7/1937 McNally 2041 8 2,769,265 11/1956 Page 20458 2,812,295 11/1957 Patrick 20458 3,031,387 4/1962 Deal et al 20458 FOREIGN PATENTS 460,476 10/ 1949 Canada. 483,776 4/1938 Great Britain.

JOHN H. MACK, Primary Examiner.

R. GOOCH, T. TUFARIELLO, Assistant Examiners. 

1. IN A PROCESS OF PRODUCING A MULTI-COLOR EFFECT ON THE SURFACE OF AN ALUMINUM ARTICLE, THE COMBINATION OF STEPS COMPRISING APPLYING A RESISTANT MASK TO A PREDETERMINED UNDYED AREA OF SAID SURFACE WHILE LEAVING ANOTHER UNDYED AREA EXPOSED, ANODIZING THE EXPOSED AREA BY TREATMENT IN AN ANODIZING ELECTROLYTIC BATH, STRIPPING THE MASK FROM THE ARTICLE, AND ANODIZING THE STRIPPED AREA OF THE SURFACE BY TREATMENT IN AN ANODIZING ELECTROLYTIC BATH, WHILE THE PREVIOUSLY ANODIZED UNDYES AREA IS ALSO EXPOSED TO THE LATTER BATH THE TWO ANODZING STEPS BEING CARRIED OUT UNDER CONDITIONS TO PRODUCE DIFFERENT COLORATIONS IN THE TWO ANODIZED AREAS RESULTING SOLELY FROM ANODIZATION OF BOTH OF SAID AREAS BY THE END OF THE SECOND ANODIZATION PERIOD. 